Step 13: Let there be light!

Step 14: Updated: Instead of wiring the lamps directly...

...wire the relay into your own outlet. Please see the specifications for the U451 for limits to the current for the devices you control.

If you have ever wanted to control electronic devices from your computer to control or regulate your environment, this instructable will guide you. In this example of computer control, a USB relay device (USBmicro http://www.usbmicro.com - U451) will control two 60 watt light bulbs from a PC program.

Step 1: Safety First!

First off - Any time that you work with 120V voltages, safety is paramount. If you are not comfortable working with mains power, please seek the assistance of someone who is.

This instructable is intended only for someone experienced and confident in wiring high voltages. Do not attempt to do this if you are not. Household current can kill or badly injure you if you who do not understand the danger.

Only the U451 relay contacts should be used for control/connection to 110V AC. The relay screw terminals are isolated from the other circuit connections. DO NOT touch the U451 when there is 110V AC present.

Step 2: Major parts

The major components used for this example instructable are:

USB relay interface USBmicro U451

two light bulbs

lamp sockets

110V AC cord

The example project will control two independent 110V AC lights with the two relays on the U451. The U451 and lights will be mounted on a wooden plank.

Step 3: Project mounting board

The lamp sockets are placed on either side of the wooden plank used for this project. The location of the lamps are copied to the plank and traced with a pen. A center line is drawn through the circle to aid in mounting the lamps.

Step 4: Board parts

Four adhesive-backed felt pads are added to the bottom side of the board. This will prevent the board from scuffing the surface that the board is placed upon.

The lamp sockets in this example setup will rest on some washers to provide some space for the wires that lead out from the under side of the socket and to the U451.

Just a heads up. The plastic covers used are intended to be flush mounted against a wall since they aren't structural. For exposed boxes you need the metal covers that don't extend past the junction boxes themselves.

My general knowledge of relays tells me that the 120v side is the side being switched on and off by the relay- essentially making it the same as the standard single pole switch in your house. And if those relay contacts are rated at 10 amps, they should be able to handle around 10 amps. The relays in components are typically purchased from other manufacturers and integrated into products by the electronics manufacturers. When they say differently about the connection to the relays being limited to 2 amps and are talking about the pcb, the 120v connection to the relays has some pcb trace going out to a separate terminal block- and that is true in this case (which would be a not-so-smart way to design a relay because it creates confusion about ratings, limits uses, and it could be done with terminals integrated into the relay to avoid all of this! ). In that case, a direct soldering of your wires to those contacts bypassing that pcb connection should suffice as described by author in comment below. Good luck, have fun, void your warranties, and BE CAREFUL! Don't hurt (enter your name here)!

A reasonable work around is to use a heavy gauge wire to connect to the soldered relay connections on the bottom of the U451 USB relay board (in pictures above). You make direct heavy connections to the relays themselves to overcome the limits of the printed circuit board.

Awesome! This might be interesting to you: we created an inverse of this idea where you can use the A/C device to control the computer. Some documentation here: http://itp.nyu.edu/~sz590/blog/2010/05/23/api-for-the-world/

Hey nice!! Can you think of a way to add current load monitoring to this... It would be cool to be able to create software to mon current load and control lighting and other circuits based on time of day and power consumption??? Any thoughts would be appreciated!

I could see hooking a few house lights up to a system like this, and when I'm on vacation, use RDP to remote into my home server, turn lights on/off to make people think house is occupied, or wire to a garage door opener and remotely open it from anywhere I have internet....so many fun possibilities!!!

I just made the plug version of this project a few days ago after seeing this instructable. It is awesome. I've tried it with some lights in my house as well as a fan a sander and a metal polisher. It's very cool to turn on and off devices using your computer. I will post a few pics of it later.

I am a qualified licensed electrician. The electrical industry uses PLC's. (programmable logic controllers). You can buy a PLC off the shelf. They are dedicated stand alone micro-controllers and far superior for electrical switching applications than using micro-controller boards and writing software. The cost factor is about equal.

Hey I am semi familiar with PLC's... Connecting them and wiring them. That said I follow the schematic provided by the engineers. Now i can figure out the schematic but I do not know how to spec the hardware. i have been trying for some time to set up a PLC to monitor the load on all forty circuits in my breaker panel and shut some off due to load, power consumption,( both peak, and cumulative,), or by remote. If you would be willing to assist me in the defining what hardware to purchase ,(PLC Lingo is greek to me,), I would greatly appreciate it.

An Ardweeny and a opto isolated triac for less than $15 USD and free software. Is there a PLC available for near that? Besides who wants to program in ladder logic...a language that was obsolete 30 years ago, but refuses to die? ;-)

How to buy somethng and use it. This is an instructible? If you had to buy relays and a microcontroller it would be an instructible. If I show you how to build something using Mindstorms is that an instructible? NO IT IS NOT. Very very dissapointing. I was hoping to learn how to build something. I was not expecting "go out and BUY a controller and hook it up as per instructions".

I thought about doing something like this, and then found that the Insteon and other home automation equipment will end up being similar in price (when it's all said and done for a useable and professional install). Plus many of the home automation equipment will carry the on/off signal over the house wiring (no need for USB) and there are even options to hook them to your router and control from an iPhone or other web device. Very cool though... and handy if you don't want to drop cash on home automation stuff..